Thermographic duplicating process



y 5, 1965 D. A. NEWMAN ETAL 3,185,087

THERMOGRAPHIC DUPLICATING PROCESS Filed Sept. 14, 1962 fly. 2

5 IMAGES 20 ORIGINAL Wm MAS- v GLAZED SURFACE 42/ l 50 FOUNDATION INVENTORS q A. Newman Boyrold. FE. Dixon United States Patent "ice 3,185,087 THElhVfGGRAPEHQ DUPLIQATING PROQESS Bonglas A. Newman, Glen Cove, and Harold F. E. Dixon,

fiouglaston, N.Y., assignors to Columbia Ribbon and This application is a ccntinuation-in-part of copending application Serial No. 57,756, filed September 22, 1960, now abandoned.

This invention relates to the method of producing duplicate transferred images on a hectograph master sheet corresponding to original images by means of infrared radiation, and more particularly to the use in such method of hectograph master sheets having extremely level working surfaces.

The art of preparing duplicate copies of imaged original sheets by means of infrared radiation is currently receiving widespread attention because of the simplicity of the method and the ease with which hectograph master sheets may be imaged to correspond with the subject matter of an original sheet.

The method, various embodiments of which are taught in U.S, Patent No. 2,808,777 to Roshkind and British Patent No. 844,695 to Ditto, generally comprises the steps of superposing original infrared radiation-absorbing images with a transfer sheet having a layer of radiationimrnune heat-transferable coloring composition and a hectograph master sheet. Next, infra-red radiation is directed against the sheets where it is absorbedv by the original images, converted to heat and conducted to the transfer layer which becomes softened and transfers to the master sheet in areas corresponding to the, superposed location of the original images.

It has been found that conventional hectograph master sheets cannot be used in the thermographic imaging process because they consist of paper stock which tends to absorb some of the infrared radiation and which insulates the heated original images from the layer of heat-transferable hectograph composition.

In the search for suitable master sheets for thermographic imaging, many thin translucent papers have been tested and, although many of .these papers appeared identical in nearly all respects including Bekk and Sheffield smoothness of their working surfaces, it was foundthat some of these papers functioned very well in the thermographic process while other seemingly-identical papers functioned poorly in that the hectograph composition transferred thereto in a spotty and irregular fashion.

it is the object of this invention to provide hectograph master sheets which may be consistently uniformly and sharply imaged in the thermographic process.

in the drawings:

FIGURE 1 is a diagrammatic cross-section, to an enlarged scale, of a segment of a master sheet according to this invention illustrating the glazed surface thereof.

PEG. 2 is a diagrammatic cross-section, to an enlarged scale, of a segment of a conventional master sheetillustrating the relatively rough surface thereof.

FIG. 3 is a diagrammatic cross-section, to an enlarged scale, of an imaged original sheet, a master sheet and a hectograph transfer sheet superposed under the effects of infrared radiation but separated for purposes of illustration.

FIG. 4 illustrates the master sheet and the transfer sheet of FIG. 1 after the transfer has taken place.

The object of this invention has been accomplished by the discovery that it is not the smoothness of the surface of the master sheet, as the term smoothness is conven- 3,185,337 l atenied May 25, 1965 tionally used in the paper art, but rather the planal levelness of the master sheet surface which is critical.

The thermographic transfer process depends upon at least two critical features. The transfer layer must have the ability of becoming soft and somewhat tacky when heated to the thermographic temperature. Also, the master sheet must be in perfect surface contact with the transfer layer so that the latter can. adhere thereto completely in areas where tackified. Where the contact is imperfect, the adhesion will be imperfect, adhesion being e'fiected principally in the raised areas of the master surface so that imperfect or spotty images will be stripped from the transfer layer onto the master sheet upon separation of the sheets.

The conventional Bekk and Sheffield smoothness tests have been found to provide no reliable indication of the planal levelness-of a paper surface of the percent of the surface of the paper which will be in perfect surface contact with the surface of the transfer layer. Both of these tests rely upon the drawing of air between the paper surface and the polished surface of a glass disc pressed thereagainst. According to these tests, fine grained or fine toothed papers, for example papers having a multitude of fine surface pits and peaks, show good smoothness figures while, glazed papers which have a high planal levelness with few valleys and peaks show up as not being smooth. This is due to the fact that although glazed papers have relatively few surface imperfections, these imperfections are comparatively deep in the form of channels which allow air to passtherethrough more readily and which therefore provide deceptive smoothness readings in both theBekk and Sheffield tests. Also the Bekk and Sheifield readings are inaccurate in the case of porous papers which allow air to pass through the paper stock rather than limiting theentry of air to the interface of the paper surface and the glassdisc.

FIGS. 1 and 2 of the drawing compare the smooth surface of a conventional calendered sheet, shown in FIG. 2, with the level surface of a glazed sheet as used according to the invention. The glazed sheet 1% of .FIG. 1 has a level surface 12 with minutely narrow channels or ripples 11 therein. These channels are a result of steam entrapment during the glazing process whereby substantially the total surface of the sheet is heat glazed and leveled against a heated metal roll while a few minute low channels are formed by small amounts of steam trapped betweenthe roll and the paper.

The calendered sheet 19 of FIG. 2 has a relatively smooth surface with numerous low valleys 21 and raised peaks 22 therein. The valleys are sufiiciently deep so that they are non-receptive or poorly receptive to a transfer layer heat softened in contact with the sheet while the raised peaks are receptive of the transfer layer but are so spaced as to receive the same in a spotty, discontinuous manner.

According to this invention, it has been discovered that master papers on which the working surface has a high planal levelness provide far superior results in the thermographic transfer process than other seemingly identical master papers which have greater Bekk and Sheffield smoothness but less planal levelness.

The planal levelness of a paper surface or the amount of contact which the surface will have with another surface pressed in contact therewith is determined by the Chapman contact test and measured by means of an Alinco Model 55 tester or the like. The theory of operation of the Chapman test is fully described in an article by S'. M. Chapman appearing in the Pulp Pa r Mag. Cart, vol. 48, No. 3, February 1947, at pages to 148.

Briefly, the test provides an optical measurement of the proportion of the surface of a paper which is in true surface contact with a smooth glass prism. This is detercontact with the prism, the light rays striking the paper will be diffracted in all directions andwill enter the glass prism directly from all directions and angles. In areas where the paper is not in true contact with the prism, there is an amount of air separating the paper surface and the prism and the light reflected back by the paper sheet must pass through this air space before entering the prism. The air refracts the light rays so that all light passing into the glass prism through an air space enters the prism at an angle no greater than 41 from the perpendicular. Using two phototubes, one to measure the amount of light from the area of the specimen in optical contact with the prism and the other to measure the amount of light entering the prism from the entire specimen, the Chapman F value is determined as a ratio of the reading of the one phototube over the reading of the other.

The glazed surface master papers suitable for use according to this invention are those having an average Chapman P value of at least about 12. The average values are arrived at by taking the average of five readings over various locations on the paper sheet which is im pressed against the glass prism under a pressure of 700 pounds per square inch.

The following table provides a comparison between the Chapman F values for the working surface of various translucent master papers suitable for use according to this invention, and Esleeck master paper currently being used in a conventional thermographic transfer process. Also, the Chapman P value for /2 mil Mylar is given as a standard:

Stock: Chapman F value Badger 8 lb. green 18.0 Badger 8 lb. reg. White 20.2 Badger 9 lb. supered white 15.9 Nekoosa-Edwards 8 1b. MG dualite white 19.0 Esleeck 100% rag white 9.6

Polyethylene terephthalate film (Mylar) /2 mil 33.9

In line with the figures of the above chart and as determined by the testing of various other translucent master papers, it has been discovered that papers having a Chapman F value at least as high as about 12 and up provide far superior results in the thermographic transfer process than papers having lower chapman values.

To demonstrate that it is planal levelness and percent contact which is critical as opposed to smoothness, the Nekoosa-Edwards 8 lb. stock of the above table was compared with the prior art Eslee-ck. 100% rag white stock in both the Bekk and Shefield testing apparatus. The Bekk smoothness of the Nekoosa-Edwards stock was 9 as compared with 163 for the Esleeck stock, and of course a higher Bekk value indicates a greater period of time required to draw a given amount of air, and thus a greater smoothness. The Sheflield smoothness of the Nekoosa- Edwards stock was 114 as compared with 68 for the Esleeck stock, and a lower Shefi'ield value indicates a smaller amount of air escaping over the paper surface, "and thus a greater smoothness. However, as demonstrated by the above chart, the Nekoosa-Edwards stock has twice the planal levelness and percent contact that the Esleeck stock has.

The master papers of this invention have a glazed working surface and are cast on a highly polished heated metal roll in a manner well known to those skilled in the art of paper manufacture. The working surface of the paper takes on the planal levelness of the polished metal roll except in areas where steam is trapped between the paper and the roll. The steam forces its way around the circumference of the roll in an attempt to escape, and as a result the paper surface is left with a few minutely narrow but comparatively deep channels which have little or no efifect upon the general image-receptivity of the overall sheet.

, against the superposed sheets.

Improved planal levelncss is accomplished when the glazing operation is carried out at slower speeds and at lower temperatures.

The present master papers are imaged in conventional manner using any suitable thermographic device such as a ThermoFax machine or a flatbed apparatus wherein a light source rich in infrared radiation may be directed The infrared radiationabsorbing images may be present on a separate original sheet or may be present on the oopy-receiving sheet. In the method illustrated by FIG. 3 of the drawing, the sheets are superposed so that the original sheet is on top and the infrared radiation-absorbing images thereon are the original images to become heated and soften corresponding areas of the transfer layer. The softened transfer layer is tacky and adheres to the level surface of the master sheet. Upon removal from the radiation source,

.. the transfer material again hardens and, when the master sheet and transfer sheet are separated, mirror images 35:: remain bonded to the master sheet in areas corresponding to the imaged areas of the original sheet.

The thus-imaged master sheet is then used in the spirit duplicating process in conventional manner to produce numerous duplicate hectograph copies of the original subject matter.

Variations and modifications may be made within the scope of the claims and portions of the improvements may be used without others.

We claim:

1. In the thermographic method of imaging a copyreceiving sheet comprising the steps of:

(a) superposing original infrared radiation-absorbing images together with a copy-receiving sheet and a transfer sheet having a layer of heat-transferable composition which does not absorb substantial amounts of infrared radiation and which is positioned in contact with the surface of the copy-receivin g sheet,

(b) exposing said superposed sheets to a light source rich in infrared radiation which is absorbed by said original images, converted to heat and conducted to corresponding areas of said heat-transferable layer to cause said areas to soften and adhere to the surface of the copy-receiving sheet, and

(c) separating said transfer and copy-receiving sheets whereby the softened areas of the transfer layer remain adhered to the copy-receiving sheet and transfer thereto; the improvement which comprises using as the copy-receiving sheet a glazed paper on which the glazed surface which is in contact with the transfer layer has a planal levelness having a Chapman F value of at least 12 measured at 700 psi.

2. The method of claim 1 wherein the copy-receiving sheet is a hcctograph master sheet and the layer of heattransferable composition on the transfer sheet comprises hectograph imaging material.

'3. The method of claim 1 wherein the original images are carried by an original sheet.

4. The method of claim 1 wherein the original images are carried by the copy-receiving sheet.

References Cited by the Examiner UNITED STATES PATENTS 2,947,585 3/61 Newman 101149.4

3,048,695 8/ 62 Russell 25 0-65 1 FOREIGN PATENTS 1,228,426 3/60 France.

DAVID KLEIN, Primary Examiner.

WILLIAM B. PENN, Examiner. 

1. IN THE THERMOGRAPHIC METHOD OF IMAGING A COPYRECEIVING SHEET COMPRISING THE STEPS OF: (A) SUPERPOSING ORIGINAL INFRARED RADIATION-ABSORBING IMAGES TOGETHER WITH A COPY-RECEIVING SHEET AND A TRANSFER SHEET HAVING A LAYER OF HEAT-TRANSFERABLE COMPOSITION WHICH DOES NOT ABSORB SUBSTANTIAL AMOUNTS OF INFRARED RADIATION AND WHICH IS POSITIONED IN CONTACT WITH THE SURFACE OF THE COPY-RECEIVING SHEET, (B) EXPOSING SAID SUPERPOSED SHEETS TO A LIGHT SOURCE RICH IN INFRARED RADIATION WHICH IS ABSORBED BY SAID ORIGINAL IMAGES, CONVERTED TO HEAT AND CONDUCTED TO CORRESPONDING AREAS OF SAID HEAT-TRANSFERABLE LAYER TO CAUSE SAID AREAS TO SOFTEN AND ADHERE TO THE SURFACE OF THE COPY-RECEIVING SHEET, AND (C) SEPARATING SAID TRANSFER AND COPY-RECEIVING SHEETS WHEREBY THE SOFTENED AREAS OF THE TRANSFER LAYER REMAIN ADHERED TO THE COPY-RECEIVING SHEET AND TRANSFER THERETO; THE IMPROVEMENT WHICH COMPRISES USING AS THE COPY-RECEIVING SHEET A GLAZED PAPER ON WHICH THE GLAZED SURFACE WHICH IS IN CONTACT WITH THE TRANSFER LAYER HAS A PLANAL LEVELNESS HAVING A CHAPMAN F VALUE OF AT LEAST 12 MEASURED AT 700 P.S.I.
 2. THE METHOD OF CLAIM 1 WHEREIN THE COPY-RECEIVING SHEET IS A HECTOGRAPH MASTER SHEET AND THE LAYER OF HEATTRANSFERABLE COMPOSITION ON THE TRANSFER SHEET COMPRISES HECTOGRAPH IMAGING MATERIAL. 